From the past, various types of technique related to traction control have been proposed, in order to prevent the tires of a moving body such as a four wheeled vehicle that has driving wheels or the like from going into the freely spinning rotational state. As one such proposed technique, a technique has been proposed that controls the torque so as to prevent increase of the slip ratio during traveling by employing a technique of model following control (refer to Patent Document #1 (and in particular to FIG. 12 thereof and the description related thereto), hereinafter termed the “prior art example”).
With this technique of the prior art example, a vehicle model of a state in which perfect adhesion is present between the driving wheel and the road surface, in other words of a state in which no slip at all is occurring, is virtually created as a reference model within a control program. And control is performed in order to make the driving wheel of the actual vehicle follow the reference model (hereinafter this will be termed “model following control”).
In concrete terms, with the technique of the prior art example, from the result of detection of the rotational speed of the driving wheel of the actual vehicle, a differential torque is calculated, which is the difference between a torque inversely calculated according to the above reference model and the torque that caused the above detected rotational speed to be generated. And, after applying a first-order delay to this calculated differential by passing it through a low pass filter, negative feedback control is performed by taking, as a correction amount, this value multiplied by a predetermined gain coefficient which is a positive value. The result is that the torque upon the driving wheel is reduced, so that increase of the slip ratio is suppressed. The reasons for suppressing increase of the slip ratio by this type of negative feedback control are as follows.
When the tire spins freely, the inertia becomes light, thereby only the driving wheel is rotating. However, when the driving wheel adheres to the road surface, the inertia becomes heavy, thereby not only the driving wheel but also the vehicle body is being driven. In other words, when the slip ratio increases, the rotational speed of the driving wheel rises.
Accordingly, in the case that slip ratio is greater than zero, inverse calculation using the rotational speed of the driving wheel with the inertia of the adhesion state gives a higher torque value than the torque that is actually applied to the driving wheel. Due to this, a differential torque value which is positive is obtained by subtracting the torque actually applied to the driving wheel from the torque obtained by the above inverse calculation. The correction amount as the result obtained by multiplying that differential torque value by a predetermined gain coefficient, a positive value as described above, becomes a positive value. Therefore, negative feedback control by using the correction amount reduces the torque applied to the driving wheel, and thus to decrease the slip ratio.
Note that, in the prior art example, it is commented that it is necessary to adjust the gain coefficient in order to take so-called dead time into consideration.